DE102007042554A1 - Nonwoven with particle filling - Google Patents

Abstract

The main body of the fleece consists of fibers forming primary pores. The main body is at least partially filled with spherical particles (3). They at least partially fill-up the pores and form regions (4) filled with particles. The novel feature is that the particles in the filled regions, form secondary pores (5). The mean diameter of the particles exceeds the mean pore size of the numerous secondary pores. The particles are uniformly-distributed over the area of the fleece. At least some filled regions are formed as a particle coating of the main body. The particles are bonded to the fleece using a binder of organic polymers. This is selected from polyvinylpyrrolidone, polyacrylic acid, polyacrylate, polymethacrylic acid, polymethacrylate, polystyrene, polyvinyl alcohol, polyvinyl acetate, polyacrylamide and their copolymers, celluloses and their derivatives, polyether, phenolic resin, melamine resin, polyurethane, nitrile rubber (NBR), styrene butadiene rubber (SBR) and latex. The melting point of the binder is below that of the particles and/or fibers. The particles have a mean diameter in the range 0.01-10 mu m. They are made from organic polymers, selected from: polypropylene, polyvinylpyrrolidone, polyvinylidene fluoride, polyester, polytetrafluoroethylene, perfluoroethylene propylene (FEP), polystyrene, styrenebutadiene copolymers, polyacrylate or nitrile butadiene polymers, polyacrylates or nitrile butadiene polymers and their copolymers. The fibers are made from organic polymers, selected from: polybutyl terephthalate, polyethylene terephthalate, polyacrylonitrile, polyvinylidene fluoride, polyetherether ketone, polyethylene naphthalate, polysulfone, polyimide, polyester polypropylene, polyoxymethylene, polyamide or polyvinyl pyrrolidone. The mean fiber length is preferably at least four times the mean fiber diameter. 90% or more of the fibers have a mean diameter of up to 12 mu m. At least 40% have a mean diameter up to 12 mu m. At least 40% of the fibers have a mean diameter of up to 8 mu m. The thickness is preferably 25 mu m. The porosity is 35% or more. Primary and secondary pores form a labyrinth structure. The secondary pore size is preferably up to 1 mu m. The ultimate tensile strength is 15 N/5 cm in the longitudinal direction. The main body is calendered.

Description

Technical area

The The invention relates to a layer comprising a main body Nonwoven fabric, wherein the base body consists of fibers and first formed by the fibers pores, wherein the base body at least partially filled with particles and wherein the particles at least partially fill the first pores and form particle filled areas.

State of the art

documents of the type mentioned are already known from the prior art. Such layers are used as separators in batteries and capacitors used, which serve the energy storage. The charge storage in batteries and capacitors takes place chemically, physically or in a mixed form, e.g. B. by chemisorption, instead.

Around an internal discharge inside the battery or the capacitor To avoid, oppositely charged electrodes are mechanically through not electronically conductive materials, so-called separators or Spacer, separated from each other. At the same time, the Separators or spacers due to their energy storage system and its application adapted porosity the transport of ionic Charge carrier of an electrolyte between the electrodes.

The Separators known from the prior art show small ones together crosslinked openings in the micrometer range. These openings should be as large as possible so that the electrolyte conductivity in the impregnated separator is as high as possible and the battery thus has a high power density. Are the openings however, too big, then metal dendrites can too a short circuit between the two actually electrically from each other lead to separating electrodes. The metal dendrites exist either from lithium or from other metals, as impurities can be present in the battery.

Of Furthermore, particles of electrically conductive Electrode materials migrate through the openings. On Reason of these operations can be a short circuit between the Electrodes arise and the self-discharge of the battery or the Condensers are greatly accelerated.

at a short circuit can be locally very high currents flow, releasing heat. These Heat can cause the separator to melt, which in turn clear the insulating effect of the separator can subside. A very fast self-discharging battery harbors this due to their high energy content and flammability of the electrolyte and other components pose a high safety risk.

One Another disadvantage of the separators known from the prior art is their lack of resistance to rising temperatures. The melting point when using polyethylene is around 130 ° C or around 150 ° C when using polypropylene.

When Causes of short circuits can shrink of the separator due to excessive temperature in the battery, metal dendrite growth by reduction of metal ions (lithium, iron, manganese or other metallic impurities), abrasion of electrode particles, cutting abrasion or broken electrode coating and direct contact of the two flat electrodes are called under pressure.

In the EP 0 892 448 A2 This is counteracted by the so-called "shut down" mechanism, which counteracts its propagation at local heating by, for example, a short circuit by suppressing the ionic conduction near the initial short circuit.Through the heat loss of the short circuit, polyethylene is heated to such an extent melts and closes the pores of the separator Higher melting polypropylene remains mechanically intact.

The US 2002/0168569 A1 describes the structure of a separator consisting of polyvinyl difluoride, which is dissolved in the manufacturing process with a solvent, mixed with silica particles and applied as a thin film. Removal of the solvent leaves a porous membrane behind.

The WO 2006/068428 A1 describes the production of separators for lithium-ion batteries using a polyolefin separator which is additionally filled with gel-like polymers and inorganic particles.

The WO 2004/021475 A1 describes the use of ceramic particles, which are formed via silicon-organic adhesion promoters and inorganic binders of oxides of the elements silicon, aluminum and / or zirconium to form a thin surface fabric.

In order to set sufficient mechanical flexibility, the ceramic particles are introduced into a support material, for example a nonwoven fabric. This reveals that WO 2005/038959 A1 ,

In order to prevent short circuits in the initial stage of the metal dendrite formation, in the WO 2005/104269 A1 the use of low-melting waxes described as admixture to a ceramic paste.

In the WO 2007/028662 A1 the addition of polymer particles having a melting point of over 100 ° C to ceramic fillers is described in order to improve the mechanical properties of the separator. The materials described are intended to serve as a separator for lithium-ion materials. Although a higher temperature resistance compared to membranes can be achieved with these separators, they can not yet prevail commercially. On the one hand, this can be due to the relatively high costs and, on the other hand, to the excessively high material thickness, which lies above 25 μm.

The WO 2000/024075 A1 describes the preparation of a membrane that can be used in fuel cells. This consists of glass fiber materials in which by means of a silicate binder fluorinated hydrocarbon polymers are fixed.

Finally, that describes JP 2005268096 A a separator for Li-ion batteries, which is prepared by the fusion of thermoplastic particles in a polyethylene / polypropylene fiber support material by heating. This has a bubble-shaped pore structure with a pore diameter of 0.1-15 microns.

Of the However, prior art does not show a cost effective separator, the at low thickness, a high porosity and a high Temperature stability and in high-performance batteries. and energy density over a wide temperature range high security requirements can be used.

Presentation of the invention

Of the Invention is therefore based on the object, a location of the beginning so-called type and further develop that they after low-cost production at a small thickness, a high Has porosity and high temperature stability.

The The present invention accomplishes the aforementioned object the features of claim 1.

After that the location is characterized in that the particles in the filled Form areas second pores, wherein the average diameter of the Particles larger than the mean pore size the plurality of second pores.

The Frequency distribution of mean pore sizes is adjusted according to the invention such that more than 50% of the second pores mean pore sizes show that lie below the mean diameter of the particles. According to the invention, it has been recognized that the pore structure an inexpensive nonwoven fabric by suitable arrangement and Selection of particles can be modified. It is very concrete it has been recognized that the porosity of the invention Position can be increased compared to polyolefin membranes, without diminishing their stability. The arrangement of a variety of particles whose mean diameter is larger as the mean pore size of the majority of the second Pores in the filled area allows the training a high porosity and thus a favored Electrolyte absorption through the nonwoven fabric. At the same time, a pore structure created in which there are almost no harmful metal dendrites can train. By the invention Arrangement of the particles can be generated by a pore structure not bubble-like, but labyrinthine and stretched pores having. In such a pore structure can dendritic Growths almost not from one side of the situation to another Form page consistently. In that regard, short circuits effectively prevented in batteries or capacitors. The inventive Location is therefore particularly suitable as a separator for batteries and capacitors with high power and energy density. The inventive Location is over a wide temperature range at high Security requirements applicable. Consequently, the aforementioned Task solved.

The Particles could be spherical. This can advantageous a predominantly densest ball packing in the first pores of the nonwoven fabric are produced. The mean pore size The majority of the second pores is essentially formed by geometric Conditions in spherical packages determined. There are infinite many possibilities to produce a densest sphere packing. Common to them is that they consist of hexagonal spherical layers. The two most important representatives are the hexagonal closest sphere packing (Layer sequence A, B, A, B, A, B) and the cubic densest sphere packing (layer sequence A, B, C, A, B, C, A). The cubic closest ball packing is also cubic face-centered spherical packing called. In a closest sphere packing, each ball has 12 nearest neighbors, six in their own shift, as well as three each above and below. They form a cuboctahedron in the cubic packing, in the Hexagonal an Antikuboktaeder. The degree of space filling a densest sphere packing is 74%. It will, however sought to produce the highest possible porosity. Therefore Not all particles in the first pores of the nonwoven fabric become one of the densest Training spherical packing. Rather, even zones loose bed of Particles occur, whereby a high porosity favors becomes.

The Particles could be homogeneous in the body be distributed. Through this specific embodiment can Short circuits are particularly effectively prevented. metal dendrites and abrasion can be due to a homogeneously occupied area almost not walk through. Furthermore, the immediate Contact of electrodes when pressurized by such Area avoided. Against this background, it is conceivable that all first pores of the nonwoven fabric are homogeneous in such a way filled with the particles are that the location predominantly medium Shows pore sizes that are smaller than the mean Diameter of the particles.

Of the Basic body could be a coating of the particles exhibit. A coating also advantageously effects the previously said suppression of short circuits. If a layer provided with a coating occurs inevitably a boundary area on the base body, at least partially filled with particles.

The Particles could through a binder with the nonwoven fabric or be interconnected. This could be the binder consist of organic polymers. The use of a binder from organic polymers allows a layer with sufficient to produce mechanical flexibility. excellent Binder properties surprisingly show polyvinylpyrrolidone.

Prefers could thermoplastic and / or thermosetting binder be used. Exemplary in this context are polyvinylpyrrolidone, Polyacrylic acid, polyacrylates, polymethacrylic acid, Polymethacrylates, polystyrene, polyvinyl alcohol, polyvinyl acetate, Polyacrylamide and copolymers of the aforementioned, cellulose and their derivatives, polyethers, phenolic resins, melamine resins, polyurethanes, Nitrile rubber (NBR), styrene butadiene rubber (SBR) and latex called.

Of the Melting point of the binder and / or the particles could be below the melting points of the fibers of the nonwoven fabric lie. By the Selecting such a binder / particle, the situation may be a so-called "shut-down mechanism" realize. Close with a "shut-down mechanism" the melting particles and / or the binder the pores of the nonwoven fabric, so that no dendritic growths through the pores and thus short circuits can occur.

In front From this background it is conceivable that mixtures of particles with different melting points are used. This can be a stepwise or stepwise closing of the pores be effected with increasing temperature.

The Particles could have a mean diameter in the range from 0.01 to 10 microns. The selection of the middle Diameter from this range has proven to be particularly beneficial proved to be short circuits due to formation of dendritic To avoid through growth or abrasion.

The Particles could be made from organic polymers, in particular of polypropylene, polyvinylpyrrolidone, polyvinylidene fluoride, polyester, Polytetrafluoroethylene, perfluoro-ethylene-propylene (FEP), polystyrene, Styrene-butadiene copolymers, polyacrylates or nitrile-butadiene polymers as well as copolymers of the aforementioned polymers. The usage Organic polymers for the particles allows a trouble-free Melting of the particles to achieve a "shut-down effect". Furthermore, a layer can be made that easily can be cut without crumbling. A crumbling The situation usually occurs when a relatively high proportion of inorganic particles is present. Against this background is conceivable mixtures of different particles or core-shell particles to use. This can be a gradual or gradual Closing the pores with increasing temperature causes become.

Conceivable is also, inorganic particles or inorganic-organic hybrid particles use. These particles do not melt below a temperature from 400 ° C. Furthermore, these particles can with basic properties to be chosen in batteries at least partially reduce the proton activity present.

The Fibers of the nonwoven fabric could be made from organic polymers, in particular of polybutyl terephthalate, polyethylene terephthalate, polyacrylonitrile, Polyvinylidene fluoride, polyetheretherketones, polyethylene naphthalate, Polysulfones, polyimide, polyester, polypropylene, polyoxymethylene, Polyamide or polyvinylpyrrolidone be made. It is also conceivable To use bicomponent fibers which include the aforementioned polymers exhibit. The use of these organic polymers allows to produce a layer that has little thermal shrinkage shows. Furthermore, these materials are largely electrochemical stable compared to those used in batteries and capacitors Electrolytes and gases.

The average length of the fibers of the nonwoven fabric could whose mean diameter is at least twice, preferably exceed many times. Through this concrete design a particularly tear-resistant nonwoven fabric can be produced, because the fibers can be swallowed together.

At least 90% of the fibers of the nonwoven fabric could have a mean diameter of at most 12 microns have. This specific embodiment allows the construction of a layer with relatively small pore sizes of the first pores. An even finer porosity can be achieved in that at least 40% of the fibers of the nonwoven fabric have an average diameter of at most 8 microns.

The Location could be through a thickness of at most 100 microns to be marked. A layer of this thickness can be still easy to wind up and allows a very safe battery operation. Preferably, the thickness could be at most 60 microns be. This thickness allows for improved windability and still a safe battery operation. Especially preferred the thickness could be at most 25 microns. With layers of such a thickness can be very compact Batteries and capacitors are built.

The Location could have a porosity of at least 25% exhibit. A layer of this porosity suppressed due to their material density particularly effective training of short circuits. Preferably, the location could be a Porosity of at least 35%. By a location This porosity can be a battery with high power density be generated. The situation described here shows high porosity nevertheless very small second pores, so that no dendritic ones Form through-growth from one side to the other side of the situation can. Against this background, it is conceivable that the second Pores form a labyrinthine structure in which no dendrite-like growths from one side to the other Training side of the situation.

The Location could be pore sizes of at most 3 microns have. The selection of this pore size has proven to be particularly beneficial to short circuits to avoid. Most preferably, the pore sizes could be at most 1 micron. Such a situation avoids particularly advantageous short circuits by metal dendrite growth, by abrasion of electrode particles and by direct contact of the electrodes when pressurized.

The Location could be a maximum tensile force in the longitudinal direction of at least 15 Newton / 5 cm. A location of this strength can be easily applied to the electrodes of a Wind up the battery without tearing.

By calendering could mechanically strengthen the layer become. The calendering causes a reduction of the surface roughness. The particles used on the surface of the nonwoven fabric show flattening after calendering.

The Location described here can be found especially in batteries and capacitors be used as a separator, since they are particularly effective short circuits prevented.

she can also be used in fuel cells as a gas diffusion layer or membrane Use, as it shows good wetting properties and Can transport liquids.

It Now there are different ways of teaching the present Invention in an advantageous manner and further develop. On the one hand to the subordinate claims, on the other hand to the following explanation of a preferred embodiment of the invention with reference to the drawing.

In Connection with the explanation of the preferred embodiment The invention with reference to the drawings are also generally preferred Embodiments and developments of the teaching explained.

Brief description of the drawing

In show the drawing

1 a scanning electron micrograph of a layer in which the particles are present in the first pores of a nonwoven fabric and form a porous particle-filled region,

2 a scanning electron micrograph of the particles of a filled area, which is designed as a coating, and

3 a greatly enlarged scanning electron micrograph of the particles of a filled area.

Embodiment of the invention

1 shows a layer with a base body made of nonwoven fabric, wherein the body of fibers 1 exists and first through the fibers 1 formed pores 2 wherein the body at least partially with particles 3 is affected and where the particles 3 the first pores 2 at least partially fill and with particles 3 filled areas 4 form.

The 3 shows a filled area 4 in an enlarged view. Regarding 3 form the particles 3 in the filled areas 4 second pores 5 from, where the mean diameter of the particles 3 greater than the average pore size of the plurality of second pores 5 is. The particles 3 are spherical and tend to form a dense sphere packing in some areas.

2 shows a coating of the particles 3 which is applied to the nonwoven fabric.

The 1 to 3 show scanning electron micrographs of a layer with a nonwoven fabric whose fibers 1 are made of polyester. The particles 3 are spherical and form partially agglomerates, which are the first pores 2 of the nonwoven fabric. The fibers 1 show a mean diameter of less than 12 microns. The layer has a thickness of 25 microns. It shows a transverse shrinkage of less than 1% at a temperature of 170 ° C.

The mean diameter of the particles 3 is 200 nm. The particles 3 consist of polyvinylidene fluoride and were made by a binder of polyvinylpyrrolidone on the fibers 1 attached.

The mean diameter of the particles 3 is calculated from the number of particles 3 in the filled area 4 determined. Preferably, the particles show 3 a narrow distribution curve, that is a mean diameter with low standard deviation. The mean pore sizes of most, namely the majority, of the second pores 5 is less than 200 nm. Below average pore size of a second pore 5 becomes the diameter of a fictional sphere 6 understood which has the same volume as the pore 5 having. The fictional sphere 6 lies between the particles in this way 3 that they are the surfaces of the neighboring particles 3 touched. Fictional balls 6 showing the dimension of the pores 5 are in 3 shown as black-bordered hollow circles.

A distribution curve whose x-axis is the mean pore size of the second pores 5 and whose y-axis shows the number or frequency of average pore sizes, would prove that more than 50% of the second pores 5 show average pore sizes that are below 200 nm.

Regarding further advantageous embodiments and developments of the teaching of the invention on the one hand to the general part of the description and on the other hand to the attached claims.

Finally be particularly emphasized that previously purely arbitrary chosen embodiment for discussion only the teaching of the invention is used, but these not limited to this embodiment.

QUOTES INCLUDE IN THE DESCRIPTION

This list The documents listed by the applicant have been automated generated and is solely for better information recorded by the reader. The list is not part of the German Patent or utility model application. The DPMA takes over no liability for any errors or omissions.

Cited patent literature

• - EP 0892448 A2 [0009]
• US 2002/0168569 A1 [0010]
• WO 2006/068428 A1 [0011]
• WO 2004/021475 A1 [0012]
• WO 2005/038959 A1 [0013]
• WO 2005/104269 A1 [0014]
• WO 2007/028662 A1 [0015]
• WO 2000/024075 A1 [0016]
• JP 2005268096 A [0017]

Claims (18)

Layer with a body made of nonwoven fabric, wherein the body of fibers ( 1 ) and first through the fibers ( 1 ) formed pores ( 2 ), wherein the main body at least partially with particles ( 3 ) and wherein the particles ( 3 ) the first pores ( 2 ) at least partially filled with particles ( 3 ) filled areas ( 4 ), characterized in that the particles ( 3 ) in the filled areas ( 4 ) second pores ( 5 ), wherein the mean diameter of the particles ( 3 ) greater than the mean pore size of the plurality of second pores ( 5 ). Layer according to claim 1, characterized in that the particles ( 3 ) are spherical. Layer according to claim 1 or 2, characterized in that the particles ( 3 ) are distributed homogeneously in the body surface. Layer according to one of claims 1 to 3, characterized in that at least a part of the filled areas ( 4 ) as a coating of the main body with the particles ( 3 ) is trained. Layer according to one of claims 1 to 4, characterized in that the particles ( 3 ) are bonded to the nonwoven fabric by a binder of organic polymers selected from the group consisting of polyvinyl pyrrolidone, polyacrylic acid, polyacrylate, polymethacrylic acid, polymethacrylate, polystyrene, polyvinyl alcohol, polyvinyl acetate, polyacrylamide and copolymers of the foregoing, cellulose and derivatives thereof, polyether, phenolic resin, melamine resin , Polyurethane, nitrile rubber (NBR), styrene butadiene rubber (SBR) and latex are selected. Layer according to one of claims 1 to 5, characterized in that the melting point of the binder below the melting points of the particles ( 3 ) and / or the fibers ( 1 ) lies. Layer according to one of claims 1 to 6, characterized in that the particles ( 3 ) have a mean diameter in the range of 0.01 and 10 microns. Layer according to one of claims 1 to 7, characterized in that the particles ( 3 ) are made of organic polymers selected from the group consisting of polypropylene, polyvinylpyrrolidone, polyvinylidene fluoride, polyester, polytetrafluoroethylene, perfluoro-ethylene-propylene (FEP), polystyrene, styrene-butadiene copolymers, polyacrylate or nitrile-butadiene polymers and copolymers of the aforementioned polymers. Layer according to one of claims 1 to 8, characterized in that the fibers ( 1 ) of the nonwoven fabric are made of organic polymers selected from the group consisting of polybutyl terephthalate, polyethylene terephthalate, polyacrylonitrile, polyvinylidene fluoride, polyether ether ketone, polyethylene naphthalate, polysulfone, polyimide, polyester, polypropylene, polyoxymethylene, polyamide or polyvinylpyrrolidone. Layer according to one of claims 1 to 9, characterized in that the average length of the fibers ( 1 ) of the nonwoven fabric whose average diameter exceeds by at least twice, preferably a multiple. Layer according to one of claims 1 to 10, characterized in that at least 90% of the fibers ( 1 ) of the nonwoven fabric have an average diameter of at most 12 μm. Layer according to one of claims 1 to 11, characterized in that at least 40% of the fibers ( 1 ) of the nonwoven fabric have an average diameter of at most 8 μm. A layer according to any one of claims 1 to 12, characterized by a thickness of at most 100 μm, preferably at most 60 microns and more preferably of 25 μm. A layer according to any one of claims 1 to 13, characterized by a porosity of at least 25%, preferably at least 35%. Layer according to one of claims 1 to 14, characterized in that the first and the second pores ( 2 . 5 ) form a labyrinthine structure. Layer according to one of claims 1 to 15, characterized by a pore size of the second pores ( 5 ) of at most 3 μm, preferably of at most 1 μm. A layer according to any one of claims 1 to 16, characterized by a maximum tensile strength of at least 15 N / 5 cm in the longitudinal direction. A layer according to any one of claims 1 to 17, characterized in that the basic body calendered is.